Epidemiologic studies have repeatedly shown that marijuana is the most commonly used illicit drug in the United States. Compared to other substances of abuse, the treatment of heavy and chronic marijuana use (dependence) has received comparatively little investigation. There is an increasing demand for marijuana treatment, but there are few controlled treatment trials that have targeted interventions for marijuana dependence. Our human laboratory studies have characterized substantial withdrawal symptoms associated with the abrupt cessation of marijuana. Laboratory studies have also found that orally administered tetrahydrocannabinol (THC) or dronabinol may have clinical utility in reducing these withdrawal effects in humans and may reduce the subjective effects of smoked marijuana. Further, an ongoing pilot study suggests that dronabinol may be administered safely in an outpatient setting. Incorporating this concept clinically, we propose a double-blind placebo-controlled 15-week trial testing the agonist dronabinol in conjunction with weekly Motivational Enhancement (MET) and Relapse Prevention (RPT) therapy. We hypothesize that reducing marijuana withdrawal symptoms will result in greater retention in treatment and lead to higher rates of abstinence in treatment seeking marijuana users. Following are the specific aims of this study: 1. To determine in marijuana-dependent individuals whether dronabinol is superior to placebo in promoting abstinence. 2. To determine in marijuana-dependent individuals whether dronabinol is superior to placebo in reducing withdrawal symptoms. 3. To determine whether the effects of dronabinol on withdrawal mediates abstinence in marijuana use / dependence (Mediational analysis). This study would be the first, double-blind, placebo-controlled study to assess the clinical utility of a cannabinoid agonist (dronabinol) for the treatment of marijuana dependence.